This invention relates to an ink jet recording sheet which is intended to be printed by an ink jet printer.
Ink jet printers, that is to say printers which form an image by firing a plurality of discrete drops of ink from one or more nozzles on to the surface of a recording sheet placed adjacent the nozzles, have recently enjoyed a large increase in sales. Such ink jet printers have the advantage that they can reproduce good quality text and images, in both monochrome and full color, can produce both reflection prints and transparencies, and are relatively inexpensive to manufacture and to operate, as compared with, for example, color laser printers, thermal wax transfer printers and dye sublimation printers. Accordingly, ink jet printers now dominate the home/small office market, and are often also used to provide color capability not available from the monochrome laser printers typically employed in larger offices.
Although modern ink jet printers can print on almost any conventional paper or similar medium, and indeed are routinely used with commercial photocopying paper for printing text, the quality of images produced by such printers is greatly affected by the properties of the medium used. To produce high quality images reliably, it is necessary that the medium (ink jet recording sheet) used rapidly absorb the ink, in order that the ink does not remain wet for an extended period, since otherwise the ink is likely to smear when successive sheets are stacked in the output tray of the printer. On the other hand, the medium should not promote excessive spreading of the ink droplet, since such spreading reduces image resolution and may result in color distortion if adjacent ink droplets intermix. The medium also should not promote "wicking", that is to say spreading of ink by capillary action through fibrous media, such as paper. The medium must be capable of absorbing the ink without substantial distortion of the medium, since otherwise unsightly "cockling" (formation of ripples and similar folds) may occur, and most observers find such distortions unacceptable. Once the ink has dried, the medium should be such that contact of the image with moist surfaces (such as sweaty fingers) does not result in bleeding of ink from the image. Finally, since the surface characteristics, such as smoothness, glossiness and feel, of the image are largely determined by the same characteristics of the medium, the medium should possess characteristics appropriate to the type of image being printed. When, as is increasingly common, an ink jet printer is used to print a digital image produced by a camera or a scanner, the medium should be smooth and possess the high gloss and smooth feel of conventional silver-halide based photographic printing paper.
It is difficult to reconcile all these demands upon an ink jet printing medium and, as shown by the literature, much research has been dedicated to improving such media. For example, U.S. Pat. No. 4,592,951 describes an ink jet recording sheet comprising a transparent support carrying a layer of cross-linked poly(vinyl alcohol). U.S. Pat. No. 4,575,465 describes an ink jet recording sheet comprising a transparent support carrying a layer formed from a mixture of vinylpyridine/vinylbenzyl quaternary ammonium salt copolymer and a hydrophilic polymer selected from the group consisting of gelatin, poly(vinyl alcohol), and hydroxypropyl cellulose, and mixtures thereof. U.S. Pat. No. 4,547,405 describes an ink jet recording sheet comprising a transparent support carrying a layer comprising a mixture of a coalesced block copolymer latex of poly(vinyl alcohol) with polyvinyl(benzyl ammonium chloride) and a water-soluble polymer selected from the group consisting of poly(vinyl alcohol), poly(vinylpyrrolidone) and copolymers thereof.
U.S. Pat. No. 4,904,519 describes an ink jet recording sheet comprising a transparent polymeric backing having on at least one major surface thereof a transparent, ink-receptive layer comprising a cross-linked, hydrolyzed copolymer of a vinyl ester comonomer selected from the group consisting of vinyl acetate, vinyl propionate and vinyl stearate, and a vinyl amide comonomer selected from the group consisting of N-vinyl pyrrolidone and vinyl acetamide, the degree of hydrolysis being from about 80 to 95%, and the cross-linking being effected by an agent selected from the group consisting of borates, titanates, dichromates and aldehydes.
U.S. Pat. No. 4,900,620 describes an ink jet recording sheet including a sheet-like substrate composed mainly of 70 to 100 wt % of wood pulp and 0 to 30 wt % of precipitated calcium carbonate and having a Stockigt sizing degree of not less than 2 seconds and not more than 25 seconds when formed into a sheet having a basis weight of 64 g/m.sup.2, and a coating layer composed mainly of white pigment, with the coating layer being formed on at least one side of the substrate at a weight of 1 to 10 g/m.sup.2. According to this patent, this sheet has a high ink absorption rate and is able to develop bright colors and sharp images.
U.S. Pat. No. 5,139,867 describes transparent image-recording elements that contain ink-receptive layers that can be imaged by the application of liquid ink dots. The ink-receptive layers contain a combination of:
(i) a vinyl pyrrolidone; PA1 (ii) particles of a polyester, namely a poly(cyclohexylenedimethylene-co-oxydiethylene isophthalate-co-sodio-sulfobenzenedicarboxylate); PA1 (iii) a homopolymer or a copolymer of an alkylene oxide containing from 2 to 6 carbon atoms; PA1 (iv) a polyvinyl alcohol; PA1 (v) a compound or a mixture of compounds having the general formula EQU R.sub.2 O(CHR.sub.1 CH.sub.2 O).sub.n R.sub.3 PA1 wherein R.sub.1 represents a hydrogen atom or a methyl group, R.sub.2 and R.sub.3 each represent a hydrogen atom, an alkyl group having a carbon number of 1 to 4 or a phenyl group, and n is an integer of 1 to 10; and PA1 (vi) inert particles. PA1 from about 20 to about 40 parts by weight of a non-derivatized poly(vinyl alcohol); PA1 from about 20 to about 40 parts by weight of an acetoacetylated poly(vinyl alcohol); PA1 from about 5 to about 15 parts by weight of an a poly(vinylbenzyl quaternary ammonium salt); PA1 from about 15 to about 30 parts by weight of poly(vinylpyrrolidone); PA1 from 0 to about 5 (most desirably about 2) parts by weight of a poly(alkyl acrylate) or poly(alkyl methacrylate); and PA1 from 0 to about 1 (most desirably about 0.2) part by weight of a surfactant.
U.S. Pat. No. 4,592,954 describes a transparency for ink jet printing comprised of a supporting substrate and thereover a coating consisting essentially of a blend of carboxymethyl cellulose, and polyethylene oxides. Also disclosed are papers for use in ink jet printing comprised of a plain paper substrate and a coating thereover consisting essentially of polyethylene oxides.
U.S. Pat. No. 5,342,688 describes an ink-receptive sheet comprising a transparent substrate bearing on at least major surface thereof an ink-receptive layer which comprises at least one imaging polymer and an effective amount of polymeric mordant, which comprises a polymethylene backbone carrying pendant aminoguanidino groups.
It has now been found that the properties of ink jet recording sheets having ink-receiving layers which contain poly(vinyl alcohol) can be improved by using as the poly(vinyl alcohol) a mixture of derivatized and non-derivatized poly(vinyl alcohol)